Improvement in the manufacture of steel



UNITED STATES V PATENT OFFICE.

IaRANz ANTON LOHAGE, or UNNA, PRUSSIA, ASSIGNOR TO E. L. BENZON,

or BOSTON, MASSACHUSETTS.

IMPROVEMENT IN THEMANUFACTURE O F STEEL.

Specification forming part of Letters Patent No. 23,139, dated March 1,1859.

To all whom it nlay-concern.-

Be it known that I, FRANZ ANTON LOHAGE, of Unna, in the Kingdom ofPrussia, a subject of the King of Prussia, have invented Improvements inthe Manufacture of Steel; and I do hereby declare that the following isa full and exact description of my said invention. W My invention ofimprovements in the manufacture of steel is based upon certaindiscoveriesllraye made in the behavior of pig or cast iron undf'iertaincircumstances, such as l while being heated or boiled in a reverheratory\furnace; and it consists in the application of the knowledge of thescientificfacts so obtained to the treatment of crude pig or cast ironor refined metal, so that guided by a close observation of the behaviorof such iron in a reverberatory or other melting furnace the workman maybe enabled with certainty and precision to decarbonize the iron to adefinite and determined extent, and leave or retain a proper amount oratomic proportion of carbon in chemical combination with the iron,and bythis means be enabled to produce steel of any required temper or degreeof hardness.

I am aware that many attempts have been made,with more orless success,to convert crude pig or cast iron into steel by decarbonizin g theformer to a certain extent; but owing to the want of an accurateknowledge of thelaws upon which are based the chemical changes that takeplace in the iron while the process of decarbonization is proceedingthese processes have heretofore been to a great extent uncertain, andthe products obtained by them have not been uniform in quality, norcould the manufacturer with any certainty rely upon producing anypredetermined and desired result.

Now, owing to the discoveries I have made of the behavior of fused ironin the paddling or reverberatory furnace I can detect and ascertain withaccuracy the chemical changes which from time to time take placeinthefurnace, and therefore I am enabled to conduct withprecision andcertainty any process and operation connected with the conversion of pigor cast iron into steel; and I have found the ordinary puddlin g orreverberatory furnace to be best adapted for carrying out the improvedprocess I have originated, because I can therein best control thechemical action of the cinder or slag upon the master pig iron, and leanalso assist the process by the mechanical action of the puddlin'g-tool,and can guide myself by the eye to attain accuracy.

It has been long known to scientific men that the different physicalproperties of pigiron, steel, and wrought-iron depend upon thepercentage of carbon they respectively contain, and that in makingpig-iron into wrought-iron in the puddling-furnace the metal at somestage of the process must contain that atomic proportion or percentageof carbon which will constitute it the substance known as steel.Starting from this known fact I commenced studying the physicalproperties of pig-iron and steel,and after various careful experimentsand observations I came to the conclusion, not only that the physicalproperties of pig-ironsuch as its non-malleability-and of variousqualities or tempers of steel-.such as their malleability and weldingpropertyas well as the different degrees of hardness of steel, dependedupon the proportion of carbon the different samples contained, but thatduring the process of manufacture the state of decarbonization re quiredto impart these physical properties to the iron might be distinctlyrecognized.

In my practical experiments to ascertain at what point ofdearbonizatioucrude pig or cast iron first became a malleable metal I discovered thatthe particlesof the metal invariably at certain stages of the processassumed certain definite forms, and that such forms of the particlesindicatedcertain definite degreesot' decarbonization and the possessionof certain definite physical properties. I thus ascertained the form theparticles of metal assumed when they possessed the physical propertiesof weldable steel, and from this I was enabled infallibly to determineat what stage ot' the process steel having such properties could beobtained. Having further determined by practical experiments the pointat which pi g-iron first becomes malleable, and which is the pointcorresponding to the highest temper of steel, and

,having carefully watched every stage of the process of decarbonization,as hereinafter more fully described, I was enabled to determine at whatpoint of decarbonization and at which corresponding form of particlescrude pig or cast iron in the puddlin g or reverberatory furnace becamefirst malleable and next weldable steel. This led to the discovery thatby closely watching the various changes and controlling or regulatingthe process I could with certainty produce in the puddling-t'urnaceevery degree of temper of steel, from the hardest steel-so hard as onlyto be titfor meltinginto cast-steel down to the softest steel, which, inthe form of German shear or cast steel,would not perceptibly harden atthe highest heat it plunged into cold water.

I will now proceed to illustrate the practical application oftheabove-mentioned discoveries, and will, to do so more clearly, explainthe manner in which it may be carried into effect in a puddling orreverberatory furnace.

I introduce into a reverberatory furnace of the usual construction(giving a preference to a furnace with a flat bottom) a convenientcharge of crude pig-iron or of refined metalsay about three hundred andsixty pounds weight-and in the first stage of the puddling process Iadopt the usual mode of operation, my object being to bring the mass toa perfect state of boiling. As the different descriptions of pig or castiron vary in their nature, they require a somewhat different treatment,which is effected, as is well known, by opening or closing dampers, asmay be required, or by adding a mixture of manganese and salt, oremploying other known means for the purpose of securing perfect boilingand a good rising of the entire mass. This point having been attained, Imake up a good fire, by means of an additional charge of coal, and workwith an open damper in order to accumulate sufficient heat for thesubsequent operations. During the boiling and raising of the mass,globular grains begin to appear on the surface of the melted cinder, andthese will increase gradually in number as the process continues. The

grains, as long as they continue of a form which I call globular, willbe found to be grains of cast-iron, having neither malleability nor awelding property, and in their motion through the cinderwill pass eachother without any apparent attraction, and even if they touch each otherwill quickly separate. At this stage of the process the cinder acts verypowerfully on the carbon of the pig-iron, the decarbonizat-ion of whichgoes on very rapidly, and it becomes important to watch the process withgreat care, when it will be seen that the particles of metal which breakthrough the cinder will gradually losetheir globular form and willbecome pointed at one end, or of what I call a pear-like form. This formof particles will indicate the presence of that amount or proportion ofcarbon in the metal which constitutes the hardest kind of steel, whichis ductile or malleable, but not weldable, and is fit only for meltinginto hard cast-steel. These pear-like grains, when they meet in theirmotion through the fluid cinder, mayperhaps come in contact with andtouch each other, but will separate, having appar ently, as yet, noattraction for each other; but as the decarbonizat-ion continues thegrains will become more and more pointed, and even elongated, and ontouching each other during their motion through the fluid mass will notseparate, as before, but will now adhere to each other, and on unitingwill sink through; the cinder. This elongated form and adhesion orfusion of the particles together will indicate the presence of thatpercentage of carbon which constitutes the hardest weldable steel. Thisstage of the process having been attained, and which may also berecognized by the workman feeling greater resistance to thepuddling-tool, it will form astarting-point for the workman, and willenable him to produce steel of the different degrees of temper andhardness required for various applications and purposes. If it bedesired to produce a bloom of the hardest weldable steel,

the process of decarbonization is only to be continued long enough afterthe appearance of the indications just described to bring the entiremass into one uniform state, after which the further progress ofdecarbonization must be stopped, either by closing the damper orotherwise.

If it be desired to produce a milder temper of steel, thedecarbonization of the mass in v the furnace must be allowed to continuefor a shorter or longer time, according to the degree of temper requiredfor the use or purpose to which the steel isintended to be applied. Assoon as the proper amount of decarbonization has been effected and thefurther progress thereof stopped the metal is to be formed into balls,care being taken always to keep the metal as much as possible immersedin or covered by the cinder, and when the balls are made they may beremoved from the furnace and forged into blooms at the welding-heat ofsteel.

What I claim as my invention, and desire to secure by Letters Patent,is-- The new or improved art of manufacturing steel of anydesired'temper or hardness, according to the various purposes or usesfor which the steel may be required, by arresting the decarbonization ofthe mass of metal 'in the furnace at certain points or stages thereof,ascertained and recognized by means of certain phenomena or externalindications manifested by the material, substantially as described.

In witness whereot'I, the said FRANZ ANTON LOHAGE, have hereunto set myhand and seal the 2d day of October, .in the year of our Lord onethousand eight hundred and fifty-eight.

FRANZ ANTON LOHAGE. [L.S.]

Witnesses "KET WALKDEN, Clerk to Newton d; Son, 66 Chancery Lane,London.

Guns. 0. JONES, 24 Royal Exchange, London.

